This is the 5th most frequent Swedish word.
det
"Det" in Swedish means "it" or "that" in English.
Here, 'det' is used as a subject pronoun to introduce the statement about the weather.
Det är kallt idag.
It is cold today.
In this context, 'det' is used as an object pronoun referring to something previously mentioned.
Kan du ge det till mig?
Can you give it to me?
Here, 'det' is an expletive subject used in an impersonal expression to introduce the statement.